In general terms, the greenhouse effect, which has been studied with wary and keen interest for as long as a century, has to do with a gradual warming of the earth's atmosphere. The warming is caused by an increase in the amount of carbon dioxide in the air around us; the CO2 holds heat from the sun instead of letting it be radiated back into space. The more of it in the atmosphere, the more difficult it is for the heat to escape. CO2 in huge amounts is constantly being released into the atmosphere by the burning of fossil fuels for energy, especially coal. In the last 25 years the concentration of CO2 has risen from about 315 parts per million to 340. Not much, you might say if you are used to dealing with such delicate chemical relationships as the right blend of vermouth and gin. But this is a significant rise, and some conservative experts believe that by the third quarter of the next century, say, 2065, the concentration will have doubled. Others say the doubling will come sooner, in less than 50 years; all agree the CO2 content will keep going up. The climatic effects of that kind of change are potentially tremendous. Temperatures would rise everywhere. According to the EPA (Environmental Protection Agency) projections, the global average temperature could go up about 3.6o Fahrenheit by 2040, and as much as 9oF by the year 2100, giving the New York of that sultry time a climate, in the words of an EPA spokesman, 'like Daytona Beach, Florida. 'Farming conditions in some chilly places that now have a very short growing season would be better, and some desert regions would get plentiful rainfall. But many areas now fruitful would be hurt. Our own Midwest would probably suffer more frequent and punishing drought, and land now dependent on irrigation would lose its sources of water. The temperature increases would cause largescale melting of ice near the poles and a rise in the sea level of about two feet in the 100 years-just for openers-with the tides of the future quite possibly necessitating 'a gradual retreat to higher ground. 'Noah, can you spare a line? The greenhouse effect_______.